11. The increase in the frequency of the triangular wave generator.
A. Ramp the amplitude of the triangular wave
B. Increase the amplitude of the triangular wave
C. Decrease the amplitude of the triangular wave
D. None of the mentioned
Answer: A
As the resistor value increase or decreases, the frequency of the triangular wave will decrease or increase, respectively. Therefore, the amplitude of the triangular wave decreases with an increase in its frequency and vice versa.
12. Which among the following op-amp is chosen for generating a triangular wave of relatively higher frequency?
A. LM741 op-amp
B. LM301 op-amp
C. LM1458 op-amp
D. LM3530 op-amp
Answer: B
The frequency of the triangular wave generator is limited by the slew rate of the op-amp. LM301 op-amp has a high slew rate.
13. What is the peak to peak (PP) output amplitude of the triangular wave?
A. VO(pp) = + VRamp + (- VRamp)
B. VO(pp) = – VRamp + (+ VRamp)
C. VO(pp) = + VRamp – (- VRamp)
D. VO(pp) = – VRamp – (+ VRamp)
Answer: C
The peak to the peak output waveform
VO(pp) = + VRamp-(-VRamp)
Where – VRamp –> Negative going ramp ;
+ VRamp–> positive-going ramp.
14. Find the capacitor value for the output frequency, fo = 2kHz & VO(pp) = 7v, in a triangular wave generator. The op-amp is 1458/741 and supply voltage = ±15v. (Take internal resistor=10kΩ)
A. 0.03nF
B. 30nF
C. 0.3nF
D. 3nF
Answer: D
Given, Vsat =15v
∴ VO(pp) = (2R2/R3) × Vsat
=> R2 =(VO(pp) ×R3) / (Vsat×2)
= [7/(2×15)]×R3 = 0.233R3
∵ Internal resistor, R2 = R1= 10kΩ
=> R3 = 0.233×10kΩ = 2.33kΩ.
So, the output frequency
fO = R3 / ( 4×R1 ×C1× R2)
=> 2khz = 2.33khz/ (4×10kΩ ×10kΩ×C1)
=> C1 = 2.33kΩ / (8×10-11)
= 2.9 ×10-9 ≅3nF.
15. Triangular waveform has
A. Rise time < fall time
B. Rise time = fall time
C. Rise time ≥ fall time
D. None of the mentioned
Answer: B
The triangular waveform has the rise time of the triangular wave always equal to its fall time, that is, the same amount of time is required for the triangular wave to swing from -VRamp to +VRamp as from +VRamp to -VRamp.
16. Output of an integrator producing waveforms of unequal rise and fall time is called
A. Triangular waveform
B. Sawtooth waveform
C. Pulsating waveform
D. Spiked waveform
Answer: B
The sawtooth waveform has unequal rise and fall times. It may rise positively many times faster than it falls negatively or vice versa.
17. Depending on the value of input and reference voltage a comparator can be named as
A. Voltage follower
B. Digital to analog converter
C. Schmitt trigger
D. Voltage level detector
Answer: D
A comparator is sometimes called a voltage level detector because, for the desired value of reference voltage, the voltage level of the input can be detected.
18. Why clamp diodes are used in the comparator?
A. To reduce output offset voltage
B. To increase the gain of the op-amp
C. To reduce input offset current
D. To protect op-amp from damage
Answer: D
The diodes protect the op-amp from damage due to excessive input voltage. Because of these diodes, the differential input voltage of the op-amp is clamped to 0.7v or -0.7 v, hence these diodes are clamp diodes.
19. How the op-amp comparator should be chosen to get the higher speed of operation?
A. Large gain
B. High slew rate
C. Wider bandwidth
D. None of the mentioned
Answer: C
The bandwidth of the op-amp comparator must be wider so that the output of the comparator can switch rapidly between saturation levels. Also, the op-amp responds instantly to any change in condition at the input.
20. How to obtain a high rate of accuracy in a comparator?
A. Input offset
B. High voltage gain
C. High CMRR
D. All of the mentioned
Answer: D
High voltage gain causes the comparator output voltage to switch between saturation levels. High CMRR rejects noise at the input terminal and input offset (voltage & current) helps to keep changes in temperature variation very slight.
21. How to keep the output voltage swing of the op-amp comparator within specific limits?
A. External resistors or diodes are used
B. External zeners or diodes are used
C. External capacitors or diodes are used
D. External inductors or diodes are used
Answer: B
To keep the output voltage swing within the specific limit, op-amps are used with external wired components such as zeners or diodes. In the resulting circuit, the outputs are limited to predetermined values.
22. Zero crossing detectors are also called as
A. Square to the sine wave generator
B. Sine to the square wave generator
C. Sine to the triangular wave generator
D. All of the mentioned
Answer: B
In zero-crossing detectors, the output waveform is always a square wave for the applied sinusoidal input signal.
23. What is the drawback of zero-crossing detectors?
A. Low-frequency signal and noise at an output terminal
B. High-frequency signal and noise at input terminal
C. Low-frequency signal and noise at input terminal
D. High-frequency signal and noise at an output terminal
Answer: C
Due to the low-frequency signal, the output voltage may not switch quickly from one saturation voltage to another. The presence of noise can fluctuate the output between two saturation voltages.
24. State a method to overcome the drawback of zero-crossing detectors?
A. Increasing input voltage
B. Use of positive feedback
C. Connect a compensating network
D. None of the mentioned
Answer: B
The drawback of zero-crossing detectors can be cured with the use of regenerative or positive feedback that causes the output to change faster and eliminate any false output transition due to noise signals at the input.
25. Name the comparator that helps to find unknown input.
A. Time marker generator
B. Zero crossing detectors
C. Phase meter
D. Window detector
Answer: D
Sometimes it is necessary to find the instant at which an unknown input is between two threshold levels. This can be achieved by a circuit called a window detector.
